The botanical alchemy uses a new class of floral genes together with three other genes responsible for flower development, to convert leaves into petals.

"We've known for a decade how to convert the flower organs into leaves," said UCSD Biology professor Martin Yanofsky. "But we haven't been able to convert leaves into flower organs. We knew we were missing a piece of the puzzle and now we know exactly what we were missing.

Last May, Professor Yanofsky and colleagues published a paper in Nature describing their discovery that a trio of identical genes called SEP genes, when mutated in concert, produce an abnormality that had been known for 2,000 years, but which scientists had never before understood. This abnormality, prized within the flower industry and known as a "double flower," results when the petals, stamens and carpels of the flower are all converted into sepals.

In the experimental plant shown below, four of the five genes needed to convert leaves into petals are turned on, leading to a partial conversion of vegetative leaves to petals.

The UCSD scientists discovered that this reiterative process of producing a flower within a flower within a flower continues indefinitely in plants with a trio of mutated SEP genes - or at least until the smallest organs of the flower can't be detected. Many roses, camellias and impatiens, as well as a host of other plants, produce these double flowers.

Now, the researchers have found in the mustard plant, Arabidopsis, that two of the SEP genes, in combination with three other genes responsible for floral development, are "sufficient to convert leaves into petals."

"It means that we should be able to convert leaves of essentially any plant into petals, which could certainly make for some very interesting looking plants," he said.

The three other genes are part of a complex known to specify the development of sepals, petals and stamens. These genes are normally not expressed in leaves, so the task of producing plants capable of expressing all five genes in leaves was an arduous one for the researchers.

"To do this, we did it one at a time and then started crossing them together, each time selecting for plants that had the additional gene introduced," said Professor Yanofsky. "Each of the genes we work with is normally active only in the flower. So we had to use genetic tricks to turn on five different genes in leaves, where they are normally not active.

"In all, the crossings alone took about a year just to finally obtain plants that expressed all five genes simultaneously in leaves. It wasn't easy, but the result was very satisfying."

Biologists have proposed for over 200 years that the sepal, petal, stamen and carpel organs that make up a typical flower represent modified leaves. But despite rapid progress by researchers around the world over the past decade in isolating key flower-control genes, no one had been able to convert leaves into each of the flower organs until now.